1. Field of the Invention
The present invention relates to a liquid crystal display device, and a timing controller and signal processing method to be used in the same and more particularly to the liquid crystal display device, and the timing controller and signal processing method to be suitably employed when an electronic device to receive and transmit data such as a circuit board having a position detection function is mounted in an interior of or in an area surrounding a liquid crystal panel.
2. Description of the Related Art
In a thin-type display device such as a liquid crystal display device and plasma display device, as resolution of a display panel becomes higher in recent years, a transmission frequency of a video signal “in” a display device also becomes higher. In response to the need for higher-speed moving picture display, a frame frequency is set to, for example, 120 Hz, thus causing a frame rate to become higher. Particularly, in the liquid crystal display device, writing is performed by the application of a voltage to a pixel of a liquid crystal panel to control a gray level for displaying, however, at the time of the voltage application to the pixel, a change in current occurs, which causes the emission of electromagnetic noise in an area surrounding the liquid crystal panel. In the liquid crystal display device, writing is done on every line of the liquid crystal panel and, therefore, the electromagnetic noise occurs by an amount corresponding to vertical resolution of the liquid crystal panel for one frame period. Moreover, an increase in added value of the display device is also required and, to achieve this aim, there are some cases where an additional circuit board having, for example, a position detecting function has to be mounted in the interior of or in an area surrounding the liquid crystal panel.
The liquid crystal display device of this kind, as shown in, for example, FIG. 8, is chiefly made up of a liquid crystal panel 1, a data driving section 2, a gate driving section 3, and a timing controller 4. In a location near to the liquid crystal panel 1, a peripheral circuit 5 configured to receive and transmit data is mounted. The liquid crystal panel 1 includes data electrodes Xi (i=1, 2, . . . , m, for example, m=1600), scanning electrodes Yj (j=1, 2, . . . , n, for example, n=1200), pixels Spi,j, and common electrodes COM. To each of the data electrodes Xi is applied a voltage corresponding to pixel data Di. To each of the scanning electrodes Yj is supplied a scanning signal Gj in a predetermined order. Each of the pixels SPi,j is mounted at the intersection of each of the data electrodes Xi and scanning electrodes Yj and is made up of a TFT (Thin Film Transistor) Q, a holding capacitor Cst, a liquid crystal layer C1c, and a common electrode COM. The holding capacitor Cst holds a voltage corresponding to an applied pixel data Di. The liquid crystal layer C1c shows diagrammatically a liquid crystal layer to display a pixel of a gray level corresponding to the pixel data Di. To the common electrode COM is applied a common voltage.
The data driving section 2 writes pixel data Di corresponding to a video signal “vf” to each of data electrodes Xi based on a video signal strobe signal STB (hereinafter, also referred to as “STB signal”) provided for every one horizontal (1H) period and drives the liquid crystal panel 1 with AC (Alternating Current) current in a predetermined manner based on a polarity inversion control signal POL (hereinafter, also referred to as “POL signal”) provided for every one horizontal (1H) period. In this case, the data driving section 2 alternately inverts the phase of the common voltage to be applied to the common electrode COM for every one dot and for every frame (between an odd-numbered frame and an even-numbered frame), for example, in a manner to correspond to the dot inversion driving method, or alternately inverts the phase of the voltage to be applied to the data electrode Xi for every one dot and for every frame (between the odd-numbered frame and the even-numbered frame). The gate driving section 3 outputs a scanning signal Gj that synchronizes to a vertical synchronizing pulse signal VSP (hereinafter, also referred to as “VSP signal”) provided for every one vertical (1V) period and drives each scanning electrode Yj in a predetermined order based on a vertical drive clock signal VCK (also called a Vertical Clock, accordingly, hereinafter, also referred to as “VCK signal”) provided for every one horizontal (1H) period. The timing controller 4 has a video signal processing section 4a and a horizontal/vertical synchronization control signal outputting section 4b. The video signal processing section 4a receives a video signal “in” and data valid period signal DE (hereinafter “DE signal”) and performs the sorting of signals and setting of a transmission voltage amplitude. The horizontal/vertical synchronization control signal outputting section 4b outputs the STB signal and the POL signal to the data driving section 2 and also outputs the VSP signal, the vertical drive clock signal VCK (or called a Vertical Clock, hereinafter “VCK signal”), a gate mask signal GOE (also called a Gate Output Enable, accordingly, hereinafter also referred to as “GOE signal”) to the gate driving section 3.
FIG. 9 is a diagram explaining each signal shown in FIG. 8. As shown in FIG. 9, the VSP signal is a reference signal to determine a frame speed of the liquid crystal panel 1 and its one cycle makes up one vertical period (1V period). The VCK signal is a clock signal to drive the gate driving section 3 during a display period d and its one cycle makes up one horizontal period (1H period). The GOE signal is used to mask an output from the gate driving section 3 and, for example, when this signal is at a low level (L), the scanning signal Gj is allowed to be outputted and, when this signal is at a high level (H) the scanning signal Gj is not allowed to be outputted. The STB signal is used to write the pixel data Di having a voltage corresponding to a gray level of the video signal “in” to the pixel SPi,j of the liquid crystal panel 1. The POL signal is used to control polarity when the pixel data Di is written to the liquid crystal display panel 1. By controlling this signal, dot inversion driving or 1H2V inversion driving is performed. Based on each of these signals, each of the scanning electrodes Yj is sequentially scanned by the gate driving section 3 and the pixel data Di having a voltage corresponding to a gray level of the video signal “in” to be written to the pixel SPi,j of the liquid crystal panel 1, thus causing a video image corresponding to the video signal “in” is displayed on the liquid crystal panel 1.
However, in such a liquid crystal display device as a first related art, there are some cases where, at the time of writing a voltage to the pixel SPi,j of the liquid crystal panel 1, if deviation of a drain voltage of a TFT among lines becomes large. (for example, such a case where, at the time of dot inversion driving, a longitudinal dot stripe is displayed), an amount of current flowing through the common electrode COM becomes large. At this point of time, noises caused by the current changes of the common electrode COM occur in an area surrounding the liquid crystal panel 1. If display causing the deviation of the drain voltage to become large among lines is performed, for example, in such a case where the longitudinal dot stripe is displayed at the time of the dot inversion driving as described above, noises caused by the current changes of the common electrode COM are generated every time when a voltage corresponding to a gray level of a video signal is written to the liquid crystal display panel 1, that is, the noises occur in every one horizontal (1H) cycle. Further, in some cases, when the liquid crystal display device is operated in a charge collection mode, as shown in FIG. 9, noises occur even at the timing of the charge collection.
As shown in FIG. 8, there is a case where a peripheral circuit 5 for receiving and transmitting data is mounted in an area surrounding the common electrode COM of the liquid crystal display device 1. Its example is a position coordinate detecting device using a liquid crystal display device as a digitizing tablet in which a change of an electromagnetic field is employed as a signal for the data receiving and transmitting. However, in the peripheral circuit 5, when a noise occurs at the time of receiving and transmitting data and, if a cycle of the occurrence of noise is shorter than the period required for receiving and transmitting data, the noise interferes with the transmission and receipt of the data, thus causing the occurrence of degradation of sensitivity for receiving data and/or malfunction in some cases. That is, the problem arises that, when a display causing variation of a drain voltage to become large among lines is performed, noises caused by writing to the pixel SPi,j of the liquid crystal panel 1 occur in the 1H cycle and, if the period for receiving and transmitting data in the peripheral circuit 5 is longer than the 1H period, the peripheral circuit 5 is always influenced by the noises caused by the writing to the pixel Spi,j, which causes the sensitivity of receiving data to be lowered and further a malfunction to occur.
A general method for suppressing the occurrence of noises from the liquid crystal panel 1 is to shield the noise generating source by a metal material or the like to separate a noise loop or to trap noises. However, a problem arises here in that, in a position coordinate detecting device using a change in electromagnetic field as a signal for receiving and transmitting data, when the liquid crystal panel 1 is shielded by the metal material, though noises from the liquid crystal panel 1 can be shielded against noises, the change in electromagnetic field to be used for its original function of detecting the position coordinate cannot be recognized. For example, in the case of a display device in which one pointer (cursor) is displayed on a display screen of the liquid crystal display panel 1 and the liquid crystal panel 1 is traced by a pointer recognizing device (for example, a touch pen) and the pointer moves by following the movement of the pointer recognizing device, in order to move the pointer on the display screen by making the pointer recognizing device follow, the pointer recognizing device has to provide the information about where the pointer recognizing device is positioned to the display device (for detection of position coordinates) and, based on this information, the pointer is moved on the display device.
Thus, in the case where the position coordinate detecting device operates by using a change in electromagnetic field, if the liquid crystal panel 1 is shielded by the metal material, the position coordinate detection signal itself is also shielded. Therefore, the method for shielding the liquid crystal panel 1 cannot be employed in the above display device and other measures must be taken. Further, it is assumed that, as resolution of a display device becomes higher and as higher-speed operation of the display panel is widely applied, timing of the occurrence of noises caused by writing of a voltage to pixels of the liquid crystal panel 1 become higher-speed (that is, the 1H period becomes short and a cycle of noise occurrence also becomes short) and, as a result, there increase fears that the above problem is more apparent. Consequently, the advent of a liquid crystal display device is expected in which degradation of signal receiving sensitivity and/or malfunction occurs in such a circuit board having a peripheral circuit for receiving and transmitting of data.
Besides the above liquid crystal display device, a display control device as a second related art of this kind is disclosed in, for example, Japanese Patent Application Laid-open No. Hei 09-154087 (Patent Reference 1). In an ordinary liquid crystal display device, a Y driver (gate driving section) is mounted, as an independent IC module, on a board and, as shown in FIG. 10B, if timing when a scan disable signal (gate mask signal) GINH is supplied to the Y driver is not proper, that is, if a delay occurs in the GINH signal, an unwanted pulse appears in a scanning signal Y1, causing the occurrence of an unwanted stripe on a display screen in some cases. Therefore, in the display control device disclosed in the above Reference 1, when video signals exceeding an image display area (number of scanning lines) are inputted, as shown in FIG. 10A, horizontal video signals are properly thinned out without causing a malfunction by masking a gate output at an appropriate position and by partially disabling writing to pixels of the liquid crystal panel. By configuring above, it is assumed that a state of no occurrence of noises for 2H periods in one frame is produced in one position or more, which causes noises caused by a change in currents not to occur.
However, the technology disclosed in the above Reference 1 has the following problems. That is, in the display control device disclosed in the Reference 1, video signals are thinned out and complemented and, therefore, video signals are partially deleted (thinned out). That is, this causes loss of video signals and, when all inputted video signals are to be displayed, another problem arises that the originally desired video display is not performed satisfactorily.